fix: only one w:displayBackgroundShape in settings.xml

The docx package always writes the element; the page-background pass
prepended a second one, breaking the CT_Settings sequence so Word
repairs the file on open — and the repair drops every header and
footer reference. The schema test's DOCX leg now builds with the
page decor, line numbering and fold marks, which covers the pass.

src/lib/export/docx.ts

@@ -1660,11 +1660,15 @@ function applyPageDecorDocx(bytes: Uint8Array, decor: PageDecor, widthPt: number
     const color = decor.background.replace('#', '').toUpperCase();
     doc = doc.replace(/(<w:document\b[^>]*>)/, `$1<w:background w:color="${color}"/>`);
     const setBytes = files['word/settings.xml'];
-    // Without this Word stores the colour but paints nothing.
+    // Without this Word stores the colour but paints nothing. The docx package already
+    // writes one; a duplicate breaks the CT_Settings sequence and Word repairs the file.
     if (setBytes) {
-      files['word/settings.xml'] = strToU8(
-        strFromU8(setBytes).replace(/(<w:settings\b[^>]*>)/, '$1<w:displayBackgroundShape/>'),
-      );
+      const settings = strFromU8(setBytes);
+      if (!settings.includes('<w:displayBackgroundShape')) {
+        files['word/settings.xml'] = strToU8(
+          settings.replace(/(<w:settings\b[^>]*>)/, '$1<w:displayBackgroundShape/>'),
+        );
+      }
     }
   }
 

tests/schema-validation.test.ts

@@ -116,7 +116,8 @@ describe.skipIf(!hasXmllint)('exported XML validates against the format schemas'
       sheet, undefined, 'add', false, opts.notesSettings, opts.props, true,
       opts.pageNumbering, opts.decor, opts.lineNumbering, true, true));
     docx = unzipSync(await buildDocx(doc, undefined, 'portrait', opts.hf, opts.language, 'A4',
-      sheet, undefined, 'add', false, opts.notesSettings, opts.props, true, opts.pageNumbering));
+      sheet, undefined, 'add', false, opts.notesSettings, opts.props, true,
+      opts.pageNumbering, opts.decor, opts.lineNumbering, true, true));
   });
 
   it('every ODF part is schema-valid (foreign namespaces stripped, as extended conformance allows)', () => {